1. Field of the Invention
The present invention relates to a laser device, and in particular, to a laser device which is able to emit light having a first wavelength and light having a second wavelength. The present invention also relates to a photoacoustic measurement device comprising the laser device.
2. Description of the Related Art
Hitherto, for example, as shown in JP2005-021380A, a photoacoustic image generation device which images the inside of a living body using a photoacoustic effect is known. In this photoacoustic image generation device, for example, the living body is irradiated with pulse light, such as pulse laser light. Inside the living body irradiated with pulse light, a living body tissue which absorbs energy of pulse light expands in volume due to heat, and an acoustic wave is generated. The acoustic wave is detected by an ultrasound probe or the like, and the inside of the living body can be imaged based on the detected signal (photoacoustic signal). In a photoacoustic image generation method, since an acoustic wave is generated in a specific optical absorber, a specific tissue in the living body, for example, a blood vessel or the like can be imaged.
A large number of living body tissues have an optical absorption characteristic which changes depending on the wavelength of light, and in general, the optical absorption characteristic is peculiar to each tissue. For example, FIG. 14 shows molecular absorption coefficients for each optical wavelength of oxygenated hemoglobin (hemoglobin bonded to oxygen: oxy-Hb) contained in a large amount in a human artery and deoxygenated hemoglobin (hemoglobin not bonded to oxygen: deoxy-Hb) contained in a large amount in a vein. The optical absorption characteristic of the artery corresponds to the optical absorption characteristic of oxygenated hemoglobin, and the optical absorption characteristic of the vein corresponds to the optical absorption characteristic of deoxygenated hemoglobin. A photoacoustic image generation method which irradiates a blood vessel portion with light having two different wavelengths by means of a difference in light absorption depending on wavelength and images the artery and the vein distinctively is known (for example, see JP2010-046215A).
For example, JP2013-089680A and JP2013-214703A describe a variable wavelength laser device which is able to emit light having two wavelengths. The laser device is an alexandrite laser light source which has a flash lamp as an excitation source, and is able to generate laser oscillation at a wavelength of 755 nm and a wavelength of 800 nm.